This is a competitive renewal application in which the authors have found that growth hormone significantly facilitated the regeneration of nitric oxide synthase containing nerves after cavernous nerve injury in a group of young rats. The authors propose to examine and compare the response to cavernous nerve injury in a group of both young and old rats and to study the effect of growth hormone and its mediator insulin-like growth factor system on the erectile mechanism. If proved beneficial in the proposed experiments, clinical application of growth hormone or IGF could become an important preventative and therapeutic manure for neurogenic impotence in humans. The specific aims are: 1: To test the hypothesis that injury to the cavernous nerve has different effects on the nonadrenergic noncholinergic vasodilator system in young and old rats. 2: To test the hypothesis that the cellular and molecular mechanisms of impotence associated with cavernous nerve injuries are due to altered gene and protein expression of NOS, TGF, NGF, IGF, FGF and adrenoreceptor in young and old rats. 3: To test the hypothesis that growth hormone facilitates regeneration of the cavernous nerve in both young and old rats. 4: To test hypothesis that the mechanism of facilitated NANC and parasympathetic nerve regeneration by growth hormone is due to production of IGF and IGFBBPs.